A brief discussion about parity checking is believed to be conducive to an understanding of the present invention. Parity checking as known in communication technology refers to the use of parity bits to check that data has been transmitted accurately. The parity bit is added to every data unit (typically seven or eight bits) that is transmitted. The parity bit for each unit is set so that all bytes have either an odd number or an even number of set bits. Assume, for example, that two devices are communicating with even parity (the most common form of parity checking). As the transmitting device sends data, it counts the number of set bits in each group of seven bits (—one data unit—). If the number of set bits is even, it sets the parity bit to 0; if the number of set bits is odd, it sets the parity bit to 1. Consequently, every byte has an even number of set bits. On the receiving side, the device checks each byte to make sure that it has an even number of set bits. If it finds an odd number of set bits, the receiver knows there was an error during transmission. The transmitting device and receiver must both agree to use parity checking and to agree on whether parity is to be odd or even. If the two sides are not configured with the same parity sense, the foregoing method parity checking in communication will not be feasible.
Parity checking is the most basic form of error detection in communications. Although parity checking detects many errors, it is not foolproof, because it cannot detect situations in which an even number of bits in the same data unit are changed due to electrical noise. Parity checking is used not only in communications but also to test memory storage devices. Many PCs, for example, perform a parity check on memory, every time a byte of data is read.
Simple bit interleaving and scrambling can be applied to make the generated symbol patterns appear more at random and with minimal self-correlation, thereby avoiding false locks at the receiver.
To some degree, bit interleaving and scrambling can combat the effects of burst noise.
A brief discussion of NICAM is believed to be conducive to an understanding of one of the applications of the present invention. NICAM stands for “Near Instantaneous Companded Audio Multiplex”, the “Near Instantaneous Companding” being due to the fact that 1 ms worth of sound data has to be input before the companding process can do its work. The “Audio Multiplex” term implies that the system is not limited just to stereo operations.
NICAM in one known form currently offers the following possibilities, auto-selected by the inclusion of a 3-bit type field in the data-stream:                One digital stereo sound channel.        Two completely different digital mono sound channels.        One digital mono sound channel and a 352 Kbit/sec data channel.        One 704 Kbit/sec data channel.        Only the first two of the ones listed are known to be in general use presently however.        
In the above referenced known form of NICAM given by way of example herein,                Sound is digitized to 14 bits accuracy at a sampling rate of 32 kHz.        The upper frequency limit of a sound channel is 15 kHz due to anti-aliasing filters at the encoder.        The 14 bit original sound samples are companded digitally to 10 bits for transmission.        
Error detection in prior art is a very common practice in digital communications. Some techniques in known art to handle errors that occur during communication are as follows:                1. A common practice is that when an error is detected at the receiver, the receiver sends back a signal to the transmitter, requesting that the signal be retransmitted, either in full or parts.        2. Some other error concealment techniques are used, which do just what the name suggests—hide the error as best as possible. Three that are noteworthy are:                    a) —using average of the 2 adjacent samples in place of the erroneous sample.            b) —using either of the 2 adjacent samples in place of erroneous sample.            c) —low pass filtering the signal which has error, to conceal the error.                        
It is known that errors are difficult to avoid in transmission channels. Accordingly, at the receiver a twofold job is generally required, including error detection and error correction. Error detection is a standard procedure in any receiver and is generally done using a parity bit as discussed supra, which is transmitted along with the data itself. But, with the presently available methodology, reliable error correction is a difficult operation to perform. Techniques mentioned supra as exemplified in point 2 (c) are merely error concealment techniques, and do not provide error correction in the real sense.
There is presently no simple known efficient correcting technique which corrects the erroneous sample instead of concealing the error.